The present disclosure relates generally to devices that can be implanted in the body, e.g., in the eye, brain or other tissue, to facilitate draining fluids from body locations. The present disclosure more particularly describes embodiments of the present invention which can be used to treat glaucoma.
Glaucoma is a significant public health problem because it is a major cause of blindness. Glaucoma is a form of optic neuropathy, i.e., a disorder of the optic nerve, that is associated with an increase in intra-ocular pressure (“IOP”) resulting from the eye lacking the ability to relieve the pressure in the anterior chamber of the eye caused by an abnormal buildup in the anterior chamber of the clear fluid known as “aqueous humor.” Aqueous humor, which is formed in the ciliary body in the posterior chamber of the eye, usually at a rate of about 2.5 microliters per minute, enters the anterior chamber through a cleft between the front of the lens and the back of the iris through the pupillary opening in the iris. When the eye is functioning normally, the aqueous humor flows out of the anterior chamber at the same or substantially the same rate as it enters and, as a result, the pressure in the eye remains safely within the normal range of about 12 to 22 mmHg. The major route of outflow of aqueous humor from the anterior chamber is through the trabecular meshwork and into Schlemm's Canal. This route is pressure dependent. When it becomes impeded, the IOP can become elevated because the inflow of aqueous humor is not balanced by outflow until the pressure in the eye rises sufficiently to overcome the impediment to outflow. The result of this increase in pressure is that pressure is transmitted to the vitreous body which, in turn, presses the retina against the choroid which compresses the blood vessels that feed the retina. In time this can result in loss of vision, both peripheral and central, and eventually lead to complete blindness.
One known mode of treatment of elevated IOP has been to implant a shunt which transmits aqueous fluid from the anterior chamber through the trabecular mesh and into Schlemm's Canal and/or other drainage channels which exist in the eye. Shunts which have been previously developed range from the very simple to the substantially complex. It has been found that even after shunts have been implanted to relieve elevated IOP, changes in IOP can occur and attempts to sense such changes in pressure and adjust flow through the shunt have been made. One cause of changes in IOP is body position such that moving from a standing position to a prone or supine position will cause changes in IOP and this, of course, means that IOP can be expected to be different depending upon whether a person is awake and normally active or asleep in a horizontal position. Embodiments of the present invention address the changes in IOP which result from changes in body position, but do not involve pressure sensing. Instead, body position is sensed and flow of aqueous humor is adjusted accordingly.